The invention relates to a method for casting metal melts from melt vessels having an outlet opening with a vertical axis for the melt that forms a pouring stream of molten metal.
Metal melts are usually allowed to emerge simply in free fall from melt vessels with bottom openings. The pouring stream of molten metal can be processed further in many ways. For example, it is possible to supply the pouring stream of molten metal to a casting mold, in which a complicated molded object is produced, or also to a block casting mold for the production of a block or ingot. To produce metal powder, it is furthermore possible to supply the pouring stream of molten metal to a centrifugal disk or an atomizer jet, which divides the pouring stream of molten metal into fine particles.
From the German Auslegeschrift 1,041,652 it is known to surround the vertical tubular elongation of the bottom opening of a crucible with a cylindrical induction coil in order to be able to interrupt the pouring stream of molten metal (using the pinch effect), so that the pouring stream of molten metal freezes due to the appropriate withdrawal of heat, and to melt the frozen "plug" subsequently once again by inductive heating with an appropriate frequency, so that casting can be recommenced.
The melt vessel may also be a so-called "funnel", in which the melt stays only a very short time for centering or for forming a pouring stream of molten metal with a defined cross section. Such a funnel usually has a ceramic interior surface or a lining to produce the required, thermal stability.
The positioning of the pouring stream of molten metal and the adjustment of the stream to one of defined cross section are required especially for so-called atomizing installations, in which a vertical pouring stream of molten metal concentrically enters an axially symmetrical jet system and in which the stream is divided into a fine powder by the supersonic flow of an inert gas. The previously used ceramic casting funnels are generally also heated in order to keep at a low value the temperature losses of the melt which arise due to contact with the inner wall of the funnel.
One of the disadvantages of these casting funnels is that the pouring stream of molten metal, on leaving the bottom opening or funnel mouth, frequently is not detached symmetrically. Moreover, the intensive contact of the melt with the interior, ceramic wall of the funnel is a disadvantage when end products must be produced which are completely free of ceramic. This requirement must be met very frequently in conjunction with heat-resistant and reactive metals and their alloys of high purity, as well as in the case of base nickel and cobalt alloys of high purity.
Attempts have also already been made to stabilize the vertical pouring stream of molten metal with higher precision without physical guiding elements. For example, by introducing probes and applying voltages the pouring stream of molten metal has been made into a conductor through which a current passes an on which magnetic force fields can act for the purpose of guiding the pouring stream. Through such measures, however, the pouring stream guidance is relatively slight and inaccurate. Moreover, the probes introduced into the pouring steam of molten metal cause spattering and turbulences thus destabilizing the pouring stream of molten metal.